Add a compile test for the element derive

Cargo.lock

@@ -3172,6 +3172,7 @@ dependencies = [
 name = "gpui_macros"
 version = "0.1.0"
 dependencies = [
+ "gpui",
  "proc-macro2",
  "quote",
  "syn 1.0.109",

crates/gpui/src/elements.rs

@@ -201,6 +201,10 @@ pub trait Element<V: View>: 'static {
     }
 }
 
+pub trait RenderElement {
+    fn render<V: View>(&mut self, view: &mut V, cx: &mut ViewContext<V>) -> AnyElement<V>;
+}
+
 trait AnyElementState<V: View> {
     fn layout(
         &mut self,

crates/gpui_macros/Cargo.toml

@@ -14,3 +14,5 @@ syn = "1.0"
 quote = "1.0"
 proc-macro2 = "1.0"
 
+[dev-dependencies]
+gpui = { path = "../gpui" }

crates/gpui_macros/src/gpui_macros.rs

@@ -283,8 +283,12 @@ pub fn element_derive(input: TokenStream) -> TokenStream {
 
     // The name of the struct/enum
     let name = input.ident;
+    let must_implement = format_ident!("{}MustImplementRenderElement", name);
 
     let expanded = quote! {
+        trait #must_implement : gpui::elements::RenderElement {}
+        impl #must_implement for #name {}
+
         impl<V: gpui::View> gpui::elements::Element<V> for #name {
             type LayoutState = gpui::elements::AnyElement<V>;
             type PaintState = ();
@@ -307,7 +311,7 @@ pub fn element_derive(input: TokenStream) -> TokenStream {
                 visible_bounds: gpui::geometry::rect::RectF,
                 element: &mut gpui::elements::AnyElement<V>,
                 view: &mut V,
-                cx: &mut gpui::ViewContext<V>,
+                cx: &mut gpui::PaintContext<V>,
             ) {
                 element.paint(scene, bounds.origin(), visible_bounds, view, cx);
             }
@@ -332,7 +336,7 @@ pub fn element_derive(input: TokenStream) -> TokenStream {
                 _: &(),
                 view: &V,
                 cx: &gpui::ViewContext<V>,
-            ) -> serde_json::Value {
+            ) -> gpui::serde_json::Value {
                 element.debug(view, cx)
             }
         }

crates/gpui_macros/tests/test.rs

@@ -0,0 +1,14 @@
+use gpui::{elements::RenderElement, View, ViewContext};
+use gpui_macros::Element;
+
+#[test]
+fn test_derive_render_element() {
+    #[derive(Element)]
+    struct TestElement {}
+
+    impl RenderElement for TestElement {
+        fn render<V: View>(&mut self, _: &mut V, _: &mut ViewContext<V>) -> gpui::AnyElement<V> {
+            unimplemented!()
+        }
+    }
+}